There are known at present various techniques of producing reinforced threads where fibres are used as the winding component. Among such techniques are various methods of open-end spinning wherein the wind-around fibres are obtained by breaking-up a fibrous lap or sliver in a fibre-separating device, and the fibres are wound or twisted around the core thread with the use of a twisting member generally employed in ringless spinning for yarn production in the form of either a spinning cup also called a spinning cell, or a disc mounted in the T-fashion on its axis of rotation, or else in other known forms, e.g. a funnel (cf. U.S. Pat. No. 3,605,395 dated 1971); since in a twisting member of any type the core thread to be wound around with fibres has to be guided through the axis of rotation of the twisting member, this axis or axle is made hollow.
Thus, the production of reinforced thread or yarn can make use of any techniques and devices for ringless open-end spinning employing the so-called once-through spinning principle according to which loose fibres are fed to the twisting member from one end thereof, and the final yarn is withdrawn from its other end through the hollow axle (cf. U.S. Pat. Nos. 3,411,283 dated 1968, and 3,501,905, dated 1970).
However, the employment of various twisting members for producing reinforced thread or yarn, be they in the form of either a spinning cup or a disc, gives rise to various specific problems needing solution. Thus, when a spinning cup is employed, there arises the problem of the quality of the thread or yarn produced, as in this case the density of winding fibres around the core thread depends solely on the tension of these fibres, maintained exclusively by the centrifugal forces which, with the practically attained speeds of rotation of spinning cups, have proved to be insufficient for ensuring the required strength of the winding. Alternatively, when a twisting member in the form of a disc is used, this gives rise to a problem of fighting the scattering of fibres from the surface of the disc under the action of the centrifugal forces, which can be solved either by ensuring reliable retaining of the fibres on the surface of the disc prior to their engagement and entanglement by the core thread, or by ensuring the engagement and entanglement by the core thread of the maximum amount of the supplied fibres prior to the action of the centrifugal forces thereupon.
The herein disclosed method and the apparatus for performing same are specifically intended for solving the last-mentioned problem.
There is known a method of producing reinforced thread or yarn and apparatus for performing this method, in that the separated fibres are retained on the surface of the disc by mechanical means including projections provided on the surface of the disc and uniformly spaced along a circle spaced from the axis of rotation of the twisting members, and through-going radial slits made in the body of the disc for the passage of the air stream and likewise uniformly angularly spaced, with at least one projection accommodated intermediate any two adjacent slits.
The projections form on the surface of the disc a rim helping to collect and retain the main stream of the fibres at the central portion of the disc, which allows for performing the thread-reinforcing process at higher speeds. This has been made possible because when the speed of rotation of the twisting member is increased, and the growing centrifugal forces tend to propel the fibres off the surface of the disc, the mechanical action of the projections opposes such propelling. Moreover, the radial slits made through the disc not only support the passage through the disc of the air stream carrying loose fibres toward the surface of the disc, but also do not resist the free passsge through the disc of lint and impurities contained in the stream of fibres, which provides for prolonged performance of the twisting member without clogging that could necessitate its cleaning.
However, all the abovementioned techniques and means for retaining fibres on the surface of the disc in the known processes and apparatus have proved to be inadequately effective, since all of them are concerned with opposing the centrifugal forces acting upon the fibres on the surface of the disc while these fibres are in the loose state, and neither of them makes use of the opportunity of positively precluding the action of the centrifugal forces on the loose fibres by engaging and twisting-in these fibres by the core thread before they come into contact with the surface of the disc, i.e. before the centrifugal forces are able to act upon them. Therefore, the percentage of fibres lost from the surface of the disc remains in these processes and apparatus relatively high, amounting to 10-12% of the total amount fed to the disc in the case of lightweight natural fibres, or even to as high as 20% in the case of heavier synthetic fibres.
This problem has been partly solved in the known method of producing reinforced thread (cf. GB Pat. No. 8608553, 08/04/86) by ringless open-end spinning, including feeding a stream of loose fibres onto the flat surface of the disc of a rotating twisting member, guiding a core thread through this disc and winding the fibres around this core thread by rotation of the twisting member, whereby the reinforced thread is produced.
This method is characterized in that it includes feeding to the twisting member and guiding through the disc at least two core threads extending at an angle to one another. Thus, these threads form in their motion a "wedge" in the path of the loose fibres, engaging and catching these fibres. Owing to the axial motion of the core threads and their joining in the axial bore of the disc, the fibres eventually become pinched by the core threads and practically are not deposited into the surface of the disc, but are drawn by the core threads into the axial bore of the disc where the centrifugal forces are virtually non-existent, and where the fibres have their ends wound around the core threads. Thus, the loose fibres coming between the core threads are driven past the zone of action of the centrifugal forces, whereby the loss and waste of fibres is reduced, and the yield of satisfactory reinforced thread is stepped up, same as the output of the machines embodying this method.
The abovedescribed effect is significantly enhanced as the number of the core threads is increased, because the more core threads take part in the process, the greater number of the "wedges" or fibre-pinching areas is formed, and the more fibres are carried past the zone of action of the centrifugal forces.
There is also known an apparatus for performing the last-described method of producing reinforced thread (cf. GB Pat. No. 8608553, 08/04/86), comprising means of separating the fibres, a twisting member including a flat disc with an axial bore, communicating with the means for separating the fibres through a fibre-guiding duct and having means for retaining the fibres and radial slits for the passage of the stream of air produced by the blades radially secured on the body of the twisting member and on the surface of the flat disc, facing the body of the twisting member, a holder for a bobbin with the core thread, a unit for winding the reinforced thread, and a guide for the core thread, overlying the plane of the flat disc.
This apparatus is characterized in that it comprises, in addition to the main guide of the core thread in the form of an opening in the housing of the apparatus, offset relative to the axial bore in the disc, a plurality of additional guides for respective additional core threads, likewise in the form of openings in the housing of the apparatus, offset relative to the axial bore in the disc. These openings through the housing of the apparatus are so arranged with respect to one another that any two adjacent core threads guided by them toward the axial bore of the disc define therebetween an angle with the apex at the inlet of the axial bore, which provides for pinching the supplied loose fibres entering this angle between the two core threads in their motion, and thus precluding the action of the centrifugal forces upon these fibres.
It is easy to conclude from the above description of the process of interaction of the core threads with the fibres in the last-mentioned method that the smaller is the angle of the "wedge" formed by the core threads, the better are the conditions of pinching the fibres by these threads, since the latter, when the angle defined by them is small, come close together even before they are joined in the axial bore of the disc. This extends the zone of pinching the fibres by the core threads and enhances their engagement capacity, and also minimizes the possibility of the fibres falling out or being taken from the "wedge" by the motion of the core threads or by the stream of air.
However, when the angles defined by the core threads are small, the area which they span across the path of the stream of loose fibres, i.e. the area of eventual engagement and pinching of the fibres by these threads, is but a fraction of the total cross-sectional area of the stream of fibres, as the latter are uniformly supplied onto the entire fibre-collecting surface of the disc defined by the projections. Consequently, but a small part of the total volume of the supplied fibres can be engaged by the core threads, whereas the greater part is beyond the area of the "wedge" of the core threads and reaches the surface of the disc, to be acted thereon by the centrifugal forces.
Therefore, the effect of reducing the loss of fibres from the surface of the disc, attained by the last-described known method and apparatus, is quite moderate, and practically does not exceed 1-2% in case of natural fibres with rough surfaces, or even 0.5-1.5% in case of smooth synthetic fibres.
Furthermore, in order to perform this known method and to attain the effect it offers, it is necessary to have at least two core threads, which means that the method can be utilized, predominantly, for production of coarse and thick reinforced threads, i.e. of threads of low Nos or counts. Higher Nos or counts of reinforced thread (when either the technology or the requirements put before the final thread would not permit having more than one core thread) cannot be produced by the known method, which curbs the range of reinforced threads that can be manufactured with the employment of this method and by apparatus performing this method.